An aircraft landing gear is generally movable between a deployed condition, for take off and landing, and a stowed condition for flight.
An actuator may be provided for moving the landing gear between the deployed and stowed conditions. These actuators are known in the art as “retraction actuators”. A retraction actuator may have one end coupled to the airframe and another end coupled to the main strut such that extension and retraction of the actuator results in movement of the main strut between deployed and stowed conditions.
One or more stay assemblies may be provided to support the orientation of the main strut when the landing gear is in the deployed condition. A stay assembly generally includes a stay and a lock link arranged to maintain the stay in a condition which corresponds to the landing gear being in the deployed condition. The lock link must be ‘broken’ to enable the stay to be folded, permitting the main strut to be moved by the retraction actuator towards the stowed condition.
It is common for landing gear to be arranged to move towards the deployed condition in the event of a failure of the retraction actuator(s). Initially, the landing gear will move by way of gravity, and in doing so the landing gear forces the stay to move towards the condition which corresponds to the landing gear being in the deployed condition. Such landing gear may include one or more ‘down locking’ springs arranged to assist in moving landing gear to the deployed condition and locking it in that state by ‘making’ the lock link. It is common on landing gear for larger aircraft to provide a pair of down locking springs on each stay assembly.
If a down locking spring fails i.e. breaks, it poses a significant safety problem due to the fact that at least one end of the down locking spring will be pivotally coupled to the lock link. As such, the pivotally coupled side of the broken spring can contact or foul other parts of the landing gear, which can result in damage to other components and in some cases may jam the landing gear mechanism.
A number of solutions have been proposed to address the above-noted problem. Firstly, it is known to provide a tether cable or telescopic tube axially within the down locking spring. In the event of a spring failure, the tether cable or telescopic tube maintains the orientation of the broken spring parts. Similarly, it is known to provide a smaller diameter spring axially within the down locking spring. However, telescopic tubes and springs may undesirably increase the weight of the landing gear. A tether cable on the other hand can cause fouling problems during the normal extension and retraction of the spring. In all cases, it can be difficult to service these parts, and it can be difficult to spot a failure.